An endoluminal prosthesis is a medical device commonly known to be used in the treatment of diseased blood vessels. An endoluminal prosthesis is typically used to repair, replace, or otherwise correct a damaged blood vessel. An artery or vein may be diseased in a variety of different ways. The prosthesis may therefore be used to prevent or treat a wide variety of defects such as stenosis of the vessel, thrombosis, occlusion, or an aneurysm.
One type of endoluminal prosthesis used in the repair of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body. Endovascular stents have become widely used for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel.
Stents are generally open ended and are radially expandable between a generally unexpanded insertion diameter and an expanded implantation diameter which is greater than the unexpanded insertion diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. The stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
A graft is another type of endoluminal prosthesis which is used to repair and replace various body vessels. Whereas a stent provides structural support to hold a damaged vessel open, a graft provides an artificial lumen through which blood may flow. Grafts are tubular devices which may be formed of a variety of material, including textiles, and non-textile materials. One type of non-textile material particularly suitable for use as an implantable prosthesis is polytetrafluoroethylene (PTFE). PTFE exhibits superior biocompatibility and low thrombogenicity, which makes it particularly useful as vascular graft material in the repair or replacement of blood vessels. In vascular applications, the grafts are manufactured from expanded PTFE (ePTFE) tubes. These tubes have a microporous structure which allows natural tissue ingrowth and cell endothelization once implanted in the vascular system. This contributes to long term healing and patency of the graft.
It is also known to combine a stent and a graft to form a composite medical device. Such a composite medical device provides additional support for blood flow through weakened sections of a blood vessel. In endovascular applications the use of a stent/graft combination is becoming increasingly important because the combination not only effectively allows the passage of blood therethrough, but also ensures the implant will remain open.
Several types of stent/graft inventions are known in the art. U.S. Pat. No. 5,151,105 issued to Kwan-Gett discloses a collapsible textile vessel sleeve with stent members positioned at opposite ends of the sleeve. The device is specifically designed to provide a vessel sleeve that is collapsible to a very small diameter in order that it may be placed in position within the abdominal or thoracic aorta by a catheter via the lumen of the femoral artery. Such a procedure obviates the need for a major surgical intervention, and reduces the risks associated with such a procedure.
Other stent/graft composite devices using a textile fabric are shown in U.S. Pat. No. 5,628,788, to Pinchuck.
As mentioned above, ePTFE may also be used as graft material in stent/graft endoprosthesis. One example of an ePTFE stent/graft composite device is shown in U.S. Pat. No. 5,700,285 issued to Myers, et al. Myers discloses a tubular intraluminal graft in the form of a tubular diametrically adjustable stent having an interior and exterior tubular covering of porous expanded polytetrafluoroethylene. The tubular covering surrounds the stent so that the stent is contained during contraction and expansion in the delivery process.
Stents are effectively used in combination with grafts as the composite endoluminal prosthesis allows blood flow through the vessel created by the graft, while the stent maintains its patency. However, as the graft covers the stent, it has a tendency to reduce the longitudinal flexibility of the composite device. Longitudinal compliance is of particular importance to such stent/graft endoluminal prosthesis as the device must be intraluminally delivered through tortuous pathways of a blood vessel to the implantation site where the stent is expanded. A reduction in longitudinal flexibility makes intraluminal delivery more difficult. Reduction in longitudinal flexibility is particularly evident with stents covered by ePTFE, which is not as compliant or flexible as textile materials.